1. Field of the Invention
This invention relates to an apparatus and a method for sterilizing devices in a container using a source of vaporizable germicide and negative pressure and more particularly, to methods which include the step of contacting the articles or the container containing the articles with a vaporizable germicide prior to exposure to negative pressure or negative pressure combined with plasma.
2. Description of the Related Art
Medical instruments have traditionally been sterilized using either heat, such as is provided by steam, or a chemical, such as formaldehyde or ethylene oxide in the gas or vapor state. Each of these methods has drawbacks. Many medical devices, such as fiberoptic devices, endoscopes, power tools, etc. are sensitive to heat, moisture, or both. Formaldehyde and ethylene oxide are both toxic gases that pose a potential hazard to healthcare workers. Problems with ethylene oxide are particularly severe, because its use requires long aeration times to remove the gas from articles that have been sterilized. This makes the sterilization cycle time undesirably long.
Sterilization using liquid hydrogen peroxide solution has been found to require high concentration of sterilant, extended exposure time and/or elevated temperatures. However, sterilization using hydrogen peroxide vapor has been shown to have some advantages over other chemical sterilization processes (see, e.g., U.S. Pat. Nos. 4,169,123 and 4,169,124). The combination of hydrogen peroxide with a plasma provides certain additional advantages, as disclosed in U.S. Pat. No. 4,643,876, issued Feb. 17, 1987 to Jacobs et al. U.S. Pat. No. 4,756,882, issued Jul. 12, 1988 also to Jacobs et al. discloses the use of hydrogen peroxide vapor, generated from an aqueous solution of hydrogen peroxide, as a precursor of the reactive species generated by a plasma generator. The combination of hydrogen peroxide vapor diffusing into close proximity with the article to be sterilized and plasma acts to sterilize the articles, even within closed packages. Further, these methods of combining hydrogen peroxide vapor with a plasma, while useful in xe2x80x9copenxe2x80x9d systems, have been found to be inadequate to effect sterilization in articles having diffusion-restricted areas, since the methods are dependent upon diffusion of the sterilant vapor into close proximity with the article before sterilization can be achieved. Thus, these methods have been found to require high concentrations of sterilant, extended exposure time and/or elevated temperatures when used on long, narrow lumens. For example, lumens longer than 27 cm and/or having an internal diameter of less than 0.3 cm have been particularly difficult to sterilize. Thus, no simple, safe, effective method of sterilizing smaller lumens exists in the prior art.
The sterilization of articles containing diffusion-restricted areas, such as long narrow lumens, therefore presents a special challenge. Methods that use hydrogen peroxide vapor that has been generated from an aqueous solution of hydrogen peroxide have certain disadvantages, because:
1. Water has a higher vapor pressure than hydrogen peroxide and will vaporize faster than hydrogen peroxide from an aqueous solution.
2. Water has a lower molecular weight than hydrogen peroxide and will diffuse faster than hydrogen peroxide in the vapor state.
Because of this, when an aqueous solution of hydrogen peroxide is vaporized in the area surrounding the items to be sterilized, the water reaches the items first and in higher concentration. The water vapor therefore becomes a barrier to the penetration of hydrogen peroxide vapor into diffusion restricted areas, such as small crevices and long narrow lumens. One cannot solve the problem by removing water from the aqueous solution and using more concentrated hydrogen peroxide, since, among other reasons, concentrated solutions of hydrogen peroxide greater than 65% by weight can be hazardous due to the oxidizing nature thereof.
U.S. Pat. No. 4,952,370 to Cummings et al. discloses a sterilization process wherein aqueous hydrogen peroxide vapor is first condensed on the article to be sterilized, and then a source of vacuum is applied to the sterilization chamber to evaporate the water and hydrogen peroxide from the article. This method is suitable to sterilize surfaces, however, it is ineffective at rapidly sterilizing diffusion-restricted areas, such as those found in lumened devices, since it too depends on the diffusion of the hydrogen peroxide vapor into the lumen to effect sterilization.
U.S. Pat. No. 4,943,414, entitled xe2x80x9cMethod for Vapor Sterilization of Articles Having Lumens,xe2x80x9d and issued to Jacobs et al., discloses a process in which a vessel containing a small amount of a vaporizable liquid sterilant solution is attached to a lumen, and the sterilant vaporizes and flows directly into the lumen of the article as the pressure is reduced during the sterilization cycle. This system has the advantage that the water and hydrogen peroxide vapor are pulled through the lumen by the pressure differential that exists, increasing the sterilization rate for lumens, but it has the disadvantage that the vessel needs to be attached to each lumen to be sterilized. In addition, water is vaporized faster and precedes the hydrogen peroxide vapor into the lumen.
In U.S. Pat. No. 5,492,672, there is disclosed a process for sterilizing narrow lumens. This process uses a multicomponent sterilant vapor and requires successive alternating periods of flow of sterilant vapor and discontinuance of such flow. A complex apparatus is used to accomplish the method. Because flow through of vapor is used, closed end lumens are not readily sterilized in the process.
Thus, there remains a need for a simple and effective method of vapor sterilization of articles having areas where diffusion of these vapors is restricted, such as long, narrow lumens.
One aspect of the invention relates to a method for sterilizing an article in a diffusion restricted environment under reduced pressure. The method includes placing the article in a container, where the container has at least one communication port and where the container is attachable to and detachable from a vacuum source through the communication port. The method also involves introducing a liquid solution of vaporizable germicide into the container, attaching the container to the vacuum source through the communication port, creating a diffusion restricted environment around the article to be sterilized, where placing, introducing, attaching, and creating can occur in any order, reducing the pressure in the container, generating germicide vapor from the vaporizable germicide, where the germicide vapor diffuses from inside the container through the communication port to outside the container, sterilizing the article in the container. The method also includes detaching the container from the vacuum source, and maintaining the sterility of the article.
Advantageously, the container is also vented through a vapor-permeable and microbe-impermeable filter. In certain embodiments, the pressure in the container is above or below atmospheric pressure when the container is detached from the vacuum source.
In an embodiment, the diffusion restricted environment is created with a diffusion restricted port.
In an embodiment, the diffusion restricted port is at least as diffusion restricted as a port having a length of 1.0 cm, a port having a cross sectional area of 63.62 mm2, or a port having a length/cross sectional area of 0.157 mmxe2x88x921.
Introducing the germicide may involve delivery of the liquid solution containing vaporizable germicide into the container via one or more methods such as injection, static soak, spray or flow-through with liquid or mist, or condensing vapor. The germicide may also be introduced by contacting the article with the liquid solution containing vaporizable germicide.
In an embodiment, the article to be sterilized is a diffusion restricted device. Preferably, the vaporizable germicide contains hydrogen peroxide. Advantageously, the pressure is reduced to below the vapor pressure of the vaporizable germicide during the reducing step.
The communication port may optionally contain a valve. Advantageously, the valve is a hinged valve. Alternatively, the valve is a septum. When the valve is a septum, the method may also include inserting a needlelike device through the septum.
Advantageously, the method may include attaching at least one additional container to the vacuum source. Preferably, the container and the additional containers each contain an article to be sterilized, and the articles can be sterilized independently, simultaneously, in a synchronized manner, in a asynchronized manner, or in a multitasking manner.
In an embodiment, an second container may be nested inside the first container. Advantageously, the second container contains a gas permeable and microbe-impermeable filter. Optionally, the second container is a flexible pouch. Preferably, a liquid solution of vaporizable germicide is in the second container before the pressure is reduced.
Another aspect of the invention concerns a method for sterilizing an article in a container under reduced pressure. The method includes placing the article in the container, where the container has at least one communication port and where the container is attachable and detachable from a vacuum source through the communication port. The method also involves attaching the container to the vacuum source through the communication port, where the placing and the attaching can occur in either order. The method includes reducing the pressure in the container with the vacuum source through the communication port, introducing germicide vapor into the container though the communication port, sterilizing the article. The method also involves detaching the container from the vacuum source and maintaining the sterility of the article.
Advantageously, the method also includes venting the container through a vapor-permeable and microbe-impermeable filter. Preferably, the pressure in the container is above or below atmospheric pressure when the container is detached from the vacuum source. In an embodiment, the germicide vapor contains hydrogen peroxide. Advantageously, the communication port contains a valve.
Preferably, at least one additional container is attached to the vacuum source. Advantageously, the container and the additional container each contain an article to be sterilized, and the articles to be sterilized can be sterilized independently, simultaneously, in a synchronized manner, in a asynchronized manner, or in a multitasking manner. In an embodiment, a second container containing at least one communication port is nested inside the container. Advantageously, the second container contains a gas permeable and microbe-impermeable filter. In an embodiment, the second container is a flexible pouch.